Ultrasound diagnostic imaging apparatus

ABSTRACT

An ultrasound diagnostic apparatus including an ultrasound probe which outputs transmission ultrasound corresponding to a drive signal, which receives reflected ultrasound from the subject and which outputs a received signal according to the reflected ultrasound; a drive signal outputter which outputs the drive signal to the ultrasound probe; a hardware processor which controls the drive signal outputter to output a first drive signal having a first drive waveform and a second drive signal having a second drive waveform that is different from the first drive waveform; a received signal generator which generates a first received signal based on the reflected ultrasound corresponding to the transmission ultrasound that is output based on the first drive signal and a second received signal based on the reflected ultrasound corresponding to the transmission ultrasound that is output based on the second drive signal; and an extractor which extracts by arithmetic of the first received signal and the second received signal a received signal component which to be used in imaging. Frequency spectrums of the first drive signal and the second drive signal have a first intensity peak on a low frequency side of a center frequency of the transmission frequency, a second intensity peak on a high frequency side of the center frequency and a third intensity peak at a frequency between a frequency corresponding to the first intensity peak and a frequency corresponding to the second intensity peak, in a frequency band included in a transmission frequency band at −20 dB of the ultrasound probe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 14/194,124, filedFeb. 28, 2014, which is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2013-041380, filed Mar. 4,2013, the entire contents of both of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an ultrasound diagnostic imagingapparatus.

2. Description of Related Art

In a conventional ultrasound diagnostic imaging apparatus, an ultrasoundprobe transmits ultrasound (transmission ultrasound) to a subject suchas a living body and the ultrasound probe converts the receivedultrasound (reflected ultrasound) into received signals to display anultrasound image based on the received signals. Since the reflectedultrasound includes information which indicates the condition inside thesubject, it is important to obtain good reflected ultrasound in order toobtain an ultrasound image of good quality. Although the image qualityof an ultrasound image can be improved by performing signal processingon the received signals, it is essentially desired that the transmissionultrasound has good quality.

Transmission ultrasound having good quality means having goodresolution. In order to realize high resolution, it is required that thetransmission ultrasound has short pulse widths. By making the frequencyband of the transmission ultrasound be a broad band or by making thefrequency of the transmission ultrasound be a high-frequency, shortpulses can be realized.

In view of the above, for example, JP 2008-43721 discloses that thewaveform of a transmission signal is arbitrarily adjusted in order toobtain the desired transmission ultrasound waveform in a conventionalultrasound diagnostic imaging apparatus.

SUMMARY OF THE INVENTION

However, in the technique described in JP 2008-43721, in order to obtainan ultrasound image of high resolution, a highly accurate and expensivetransmission drive apparatus which can form an arbitrary waveform andcontrol the waveform formation using a circuit is required. On the otherhand, since such expensive transmission drive apparatus cannot be usedin a small and low-cost ultrasound diagnostic imaging apparatus, thereis no choice but to compromise on image quality.

In view of the above circumstances, an object of the present inventionis to provide an ultrasound diagnostic imaging apparatus which canmaintain high resolution while keeping the cost down.

In order to realize at least one of the above objects, an ultrasounddiagnostic imaging apparatus reflecting one aspect of the presentinvention includes an ultrasound probe which outputs transmissionultrasound toward a subject due to a pulse signal being input and whichoutputs a received signal by receiving reflected ultrasound from thesubject, and a transmission unit which makes the ultrasound probegenerate the transmission ultrasound by outputting a pulse signal whosedrive waveform is formed of rectangular waves, and a frequency powerspectrum of the pulse signal has intensity peaks in a frequency bandincluded in a transmission frequency band at −20 dB of the ultrasoundprobe on a low frequency side and a high frequency side of a centerfrequency of the transmission frequency band, respectively, andintensity of a frequency region between the intensity peaks is −20 dB orgreater with a maximum value of intensity among the intensity peaksbeing a reference.

Preferably, the transmission unit outputs pulse signals of differentdrive waveforms on a same scanning line for a plurality of times with atime interval therebetween, and the ultrasound diagnostic imagingapparatus further includes an image generation unit which combinesreceived signals each of which obtained from the reflected ultrasound ofthe transmission ultrasound generated by each output of pulse signal andgenerates ultrasound image data on a basis of a composite pulse signal.

Preferably, in the frequency power spectrum of the pulse signal,intensity of a frequency component at at least one intensity peak amongthe intensity peaks is greater than intensity of a frequency componentat a frequency same as the center frequency in the transmissionfrequency band at −20 dB of the ultrasound probe.

Preferably, the frequency power spectrum of the pulse signal includestwo or more intensity peaks in the transmission frequency band on thehigh frequency side of the center frequency of the transmissionfrequency band at −20 dB of the ultrasound probe.

Preferably, the pulse signal is formed of rectangular waves of fivevalues or less.

Preferably, in the ultrasound probe, a fractional bandwidth at −20 dB is110% or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the appended drawings whichare given byway of illustration only, and thus are not intended as adefinition of the limits of the present invention, and wherein:

FIG. 1 is a drawing showing an outer structure of an ultrasounddiagnostic imaging apparatus;

FIG. 2 is a block diagram showing a schematic configuration of theultrasound diagnostic imaging apparatus;

FIG. 3 is a block diagram showing a schematic configuration of atransmission unit;

FIG. 4 is a drawing for explaining a drive waveform of a pulse signal;

FIG. 5A is a drawing for explaining an example of a transmissionbandwidth shape of an ultrasound probe;

FIG. 5B is a drawing for explaining an example of a drive waveform of apulse signal which is output from the transmission unit;

FIG. 5C is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 5B;

FIG. 5D is a drawing showing a result of frequency analysis performed ontransmission ultrasound which is output from the ultrasound probe;

FIG. 6 is a drawing for explaining a transmission bandwidth of theultrasound probe;

FIG. 7A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 7B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 7A;

FIG. 8A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 8B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 8A;

FIG. 9A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 9B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 9A;

FIG. 10A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 10B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulses signal shown in FIG. 10A;

FIG. 11A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 11B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 11A;

FIG. 12A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 12B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 12A;

FIG. 13A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 13B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 13A;

FIG. 14A is a drawing for explaining an example of a drive waveform of apulse signal;

FIG. 14B is a drawing showing frequency power spectrum obtained byperforming frequency analysis on the pulse signal shown in FIG. 14A;

FIG. 15 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 16 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 17 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 18 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 19 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 20 is a drawing for explaining spectrum of transmission ultrasound;

FIG. 21 is a drawing for explaining spectrum of transmission ultrasound;and

FIG. 22 is a drawing for explaining spectrum of transmission ultrasound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the ultrasound diagnostic imaging apparatus according to anembodiment of the present invention will be described with reference tothe drawings. However, the scope of the invention is not limited to theexamples shown in the drawings. In the following description, samenumeral references are used for similar functions and similarconfigurations and their descriptions are omitted.

As shown in FIGS. 1 and 2, the ultrasound diagnostic imaging apparatus Saccording to an embodiment includes an ultrasound diagnostic imagingapparatus main body 1 and an ultrasound probe 2. The ultrasound probe 2transmits ultrasound (transmission ultrasound) to a subject such as aliving body (not shown in the drawing) and receives reflected wave(reflected ultrasound: echo) of the ultrasound reflected off thesubject. The ultrasound diagnostic imaging apparatus main body 1 isconnected with the ultrasound probe 2 via a cable 3. The ultrasounddiagnostic imaging apparatus main body 1 transmits drive signals whichare electric signals to the ultrasound probe 2 to make the ultrasoundprobe 2 transmit transmission ultrasound to a subject and visualizes theinside state of the subject as an ultrasound image on the basis of thereceived signals which are electric signals generated in the ultrasoundprobe 2 according to the reflected ultrasound from inside of the subjectreceived by the ultrasound probe 2.

The ultrasound probe 2 includes transducers 2 a formed of piezoelectricelements and for example, the transducers 2 a are aligned in aone-dimensional array in an orientation direction. In the embodiment,for example, an ultrasound probe 2 provided with 192 transducers 2 a isused. Here, the transducers 2 a may be aligned in a two-dimensionalarray. Further, the number of transducers 2 a can be set arbitrarily.Although a linear scanning type electronic-scanning probe is used as theultrasound probe 2 in the embodiment, either an electronic-scanning typeor a mechanic-scanning type can be used. Further, any type of linearscanning, sector scanning and convex scanning can be adopted. In theembodiment, the transmission ultrasound having high resolution can beefficiently obtained by using an ultrasound probe which can transmitultrasound in a broad band with good sensitivity, and an even betterultrasound image can be obtained. The bandwidth of the ultrasound probecan be set arbitrarily; however, it is preferred that the fractionalbandwidth at −20 dB is 110% or greater.

As shown in FIG. 2, the ultrasound diagnostic imaging apparatus mainbody 1 includes an operation input unit 11, a transmission unit 12, areception unit 13, an image generation unit 14, an image processing unit15, a DSC (Digital Scan Converter) 16, a display unit 17 and a controlunit 18, for example.

The operation input unit 11 includes various types of switches, buttons,a track ball, a mouse, a key board and the like for inputting commandsfor instructing the start of diagnosis and data such as personalinformation relating to a subject, etc. and the operation input unit 11outputs operation signals to the control unit 18.

The transmission unit 12 is a circuit for supplying drive signals whichare electric signals to the ultrasound probe 2 via the cable 3 accordingto the control of the control unit 18 to make the ultrasound probe 2generate transmission ultrasound. More specifically, as shown in FIG. 3,the transmission unit 12 includes a clock generator circuit 121, a pulsegenerator circuit 122, a duty setting unit 123 and a delay circuit 124,for example.

The clock generator circuit 121 is a circuit for generating a clocksignal for deciding the transmission timing and the transmissionfrequency of a drive signal.

The pulse generator circuit 122 is a circuit for generating a pulsesignal as a drive signal in a predetermined cycle. The pulse generatorcircuit 122 can generate a pulse signal of rectangular waves byswitching between 5 values of voltage (+HV/+MV/0/−MV/−HV) and output thevoltage as shown in FIG. 4, for example. Here, the amplitude of thepulse signal is made so as to be the same in the positive polarity andin the negative polarity. However, this is not limitative in any way. Inthe embodiment, a pulse signal is output by switching among five voltagevalues. However, the voltage values are not limited to five values andcan be set to arbitrary number of values, although, the number of valuesis desired to be five values or less. In such way, the degree of freedomfor controlling the frequency components can be improved at a low costand transmission ultrasound having even higher resolution can beobtained.

The duty setting unit 123 sets the duty ratio of a pulse signal which isoutput from the pulse generator circuit 122. That is, the pulsegenerator circuit 122 outputs a pulse signal of a pulse waveformaccording to the duty ratio set by the duty setting unit 123. The dutyratio can be changed by the input operation performed on the operationinput unit 11.

In the embodiment, the duty setting unit 123 sets the duty ratio of apulse signal so that a peak included in the transmission frequency bandof the ultrasound probe 2 is generated in each of the low frequency sideand the high frequency side of the center frequency of the transmissionfrequency band of the ultrasound probe 2. At this time, the duty settingunit 123 sets the duty ratio of the pulse signal so that the sensitivityof the ultrasound probe at the transmission frequency band of −20 dB be−20 dB or greater.

Here, more details will be described with reference to FIG. 5. FIG. 5Ashows an example of a transmission bandwidth shape Pr of the ultrasoundprobe 2. FIG. 5B shows an example of a drive waveform of a pulse signalwhich is output from the transmission unit 12. FIG. 5C shows a frequencypower spectrum obtained by performing frequency analysis (FFT) on thepulse signal shown in FIG. 5B. FIG. 5D shows the result of performingthe frequency analysis (FFT) on the transmission ultrasound output fromthe ultrasound probe 2.

For example, with respect to the ultrasound probe 2 as shown in FIG. 5A,the peak frequency is 14.2 MH, the minimum frequency (FL20) at −20 dB is3.4 MHz, the maximum frequency (FH20) at −20 dB is 21.2 MHz, the centerfrequency (FC20) is 12.3 MHz and the fractional bandwidth at −20 db is145%.

To such ultrasound probe 2, a pulse signal Sg having a drive waveform asshown in FIG. 5B is applied, for example. The pulse signal Sg is formedof rectangular waves and can be generated by switching between fivevoltage values. The frequency power spectrum obtained by performing thefrequency analysis on the pulse signal Sg has, as shown in FIG. 5C, oneintensity peak (PK1: 5.8 MHz) on the low frequency side of the centerfrequency (FC20) in the transmission frequency band at −20 dB of theultrasound probe 2 and has two intensity peaks (PK2: 13.2 MHz, PK3: 19.2MHz) on the high frequency side (here, Sf in FIG. 5C shows the analysisresult). That is, if a pulse signal having the drive waveform as shownin FIG. 5B is applied to the ultrasound probe 2 having thecharacteristics as shown in FIG. 5A, the peaks (PK1 to PK3) included inthe transmission frequency band of the ultrasound probe 2 are generatedon the low frequency side and on the high frequency side of the centerfrequency (FC20) in the transmission frequency band (FL20-FH20) of theultrasound probe 2. Intensities at the intensity peaks (P1: 3.8 dB, P2:2.0 dB, P3: 1.4 dB) are greater than the intensity (1.1 dB) of thefrequency component at the frequency (12.3 MHz) which is the same as thecenter frequency of the transmission frequency band of the ultrasoundprobe 2. Further, the intensities between the intensity peaks are −20 dBor greater with the intensity at PK1, which is the maximum intensityvalue among the intensity peaks, being the reference. As a result, thetransmission ultrasound having the characteristics as shown in FIG. 5Dis output from the ultrasound probe 2.

The transmission bandwidth shape of the ultrasound probe 2 and the drivewaveform of the pulse signal in the embodiment is not limitative in anyway and can be arbitrarily set within a feasible range.

Further, although all of the plurality of intensity peaks in the pulsesignal are greater than the intensity of the frequency component at thefrequency which is the same as the center frequency of the transmissionfrequency band of the ultrasound probe 2 in the embodiment, it issufficient that at least one or more of the intensity peaks is greaterthan the intensity of the frequency component at the frequency which isthe same as the center frequency of the transmission frequency band ofthe ultrasound probe 2.

Furthermore, although a pulse signal which gives two intensity peaks onthe high frequency side of the center frequency (FC20) in thetransmission frequency band of the ultrasound probe 2 is output in theembodiment, there may be three or more of such intensity peaks. When apulse signal which gives two or more intensity peaks on the highfrequency side of the center frequency (FC20) in the transmissionfrequency band of the ultrasound probe 2 is used, a pulse signal havingeven broader bandwidth on the high frequency side can be output. A pulsesignal which gives only one intensity peak on the high frequency side ofthe center frequency (FC20) in the transmission frequency band of theultrasound probe 2 may also be used.

The delay circuit 124 is a circuit for setting delay times intransmission timings of drive signals for individual paths correspondingto the transducers and delays the transmission of the drive signals forthe set delay times to concentrate the transmission beams constituted oftransmission ultrasound.

The transmission unit 12 configured as described above sequentiallyswitches the transducer 2 a which supplies a drive signal among theplurality of transducers 2 a by a predetermined number of transducers 2a for every transmission and reception of ultrasound according to thecontrol of the control unit 18 and supplies drive signals to theselected plurality of transducers 2 a to perform scanning.

In the embodiment, pulse inversion can be performed in order to extractthe after-mentioned harmonic component. That is, when performing pulseinversion, the transmission unit 12 can transmit the first pulse signaland the second pulse signal whose polarity is inverse of that of thefirst pulse signal on the same scanning line with some time intervaltherebetween. At this time, the second pulse signal formed by changingat least one of the plurality of duties of the first pulse signal toinverse its polarity may be transmitted. Further, the second pulsesignal may be a signal formed by performing time inversion on the firstpulse signal.

The reception unit 13 is a circuit for receiving received signals whichare electric signals from the ultrasound probe 2 via the cable 3 incompliance with the control of the control unit 18. The reception unit13 is provided with an amplifier, an A/D conversion circuit and aphasing addition circuit, for example. The amplifier is a circuit foramplifying the received signals at a preset amplification factor for theindividual paths corresponding to the transducers 2 a. The A/Dconversion circuit is a circuit for performing analog/digital conversion(A/D conversion) of the amplified received signals. The phasing additioncircuit is a circuit for adjusting time phases of the received signalsto which A/D conversion is performed by applying the delay timed to theindividual paths respectively corresponding to the transducers 2 a andgenerating sound ray data by adding the adjusted received signals (phaseaddition).

The image generation unit 14 generates B-mode image data by performingenvelope detection, logarithmic amplification and the like on the soundray data from the reception unit 13 and performing brightness conversionby performing gain adjustment and the like. In other words, B-mode imagedata is data where intensities of received signals are expressed interms of brightness. The B-mode image data which is generated in theimage generation unit 14 is transmitted to the image processing unit 15.Further, the image generation unit 14 includes the harmonic componentextraction unit 14 a.

The harmonic component extraction unit 14 a performs pulse inversion andextracts harmonic components from the received signals which are outputfrom the reception unit 13. In the embodiment, a second harmoniccomponent can be extracted by the harmonic component extraction unit 14a. A second harmonic component can be extracted by filtering afteradding (composition) the received signals obtained from the reflectedultrasounds corresponding to the two transmission ultrasoundsrespectively generated from the above mentioned first pulse signal andsecond pulse signal and removing the fundamental wave component includedin the added received signal.

The image processing unit 15 includes an image memory unit 15 aconstituted of a semiconductor memory such as a DRAM (Dynamic RandomAccess Memory). The image processing unit 15 stores B-mode image dataoutput from the image generation unit 14 in the image memory unit 15 ain frame units. The image data in frame units may be called ultrasoundimage data or frame image data. The image processing unit 15 arbitrarilyreads out the ultrasound image data stored in the image memory unit 15 aand outputs the ultrasound image data to the DSC 16.

The DSC 16 converts the ultrasound image data received by the imageprocessing unit 15 into an image signal of television signal scan modeand outputs the image signal to the display unit 17.

As for the display unit 17, display apparatuses such as a LCD (LiquidCrystal Display), a CRT (Cathode-Ray Tube) display, an organic EL(Electronic Luminescence) display, an inorganic EL display or a plasmadisplay can be applied. The display unit 17 displays an ultrasound imageon the display screen according to the image signal output from the DSC16.

The control unit 18 includes a CPU (Central Processing Unit), a ROM(Read Only Memory) and a RAM (Random Access Memory), for example. Thecontrol unit 18 reads out and opens various types of programs such as asystem program stored in the ROM in the RAM and collectively controlsthe operations of the components in the ultrasound diagnostic imagingapparatus S in compliance with the opened programs.

The ROM is configured of a non-volatile memory of semiconductor or thelike, and stores a system program corresponding to the ultrasounddiagnostic imaging apparatus S, various types of processing programswhich can be executed on the system program, various types of data andthe like. These programs are stored in the forms of program codes whichcan be read by a computer and the CPU sequentially executes theoperations according to the program codes.

The RAM forms a work area in which various types of programs to beexecuted by the CPU and data relating to these programs are to be storedtemporarily.

Embodiment 1

Hereinafter, the present invention will be described in detail in termsof embodiment examples. However, it is needless to say that the presentinvention is not limited to the embodiment examples in any way.

Embodiment Example 1

First, as for the above mentioned ultrasound probe 2, an ultrasoundprobe having the following characteristics is used, the characteristicsbeing: the minimum frequency (FL20) at −20 dB in transmission is 3.4MHz; the maximum frequency (FH20) at −20 dB in transmission is 21.2 MHz;the center frequency (FC20) is 12.3 MHz and the fractional bandwidth at−20 dB in transmission is 145%. This ultrasound probe is referred to asthe ultrasound probe A. The line A in FIG. 6 shows the transmissionbandwidth shape of the ultrasound probe A. In FIG. 6, the horizontalaxis indicates frequency and the vertical axis indicates sensitivity.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 7A, and this is referred to as the drive waveform 1.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 7B. In FIG. 7A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG. 7B,the horizontal axis indicates frequency and the vertical axis indicatessignal intensity. When frequency analysis is performed on this drivewaveform, the minimum frequency at −20 dB is 0.6 MHz, the maximumfrequency at −20 dB is 20 MHz and the center frequency is 9.7 MHz.Further, this drive waveform gives two intensity peaks in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 5.2 MHzand the intensity is −2.0 dB and at the second peak (peak 2), thefrequency is 14.8 MHz and the intensity is 1.2 dB. Further, thefrequency component at the frequency (12.3 MHz) same as the centerfrequency in the transmission frequency band of the ultrasound probe Ahas the intensity of −0.4 dB. The spectrum of the transmissionultrasound which is output due to the pulse signal of the drive waveform1 being applied to the ultrasound probe A is shown in FIG. 15.

Embodiment Example 2

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 8A, and this is referred to as the drive waveform 2.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 8B. In FIG. 8A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG. 8B,the horizontal axis indicates frequency and the vertical axis indicatessignal intensity. When frequency analysis is performed on this drivewaveform, the minimum frequency at −20 dB is 0.4 MHz, the maximumfrequency at −20 dB is 27.2 MHz and the center frequency is 13.8 MHz.Further, this drive waveform gives three intensity peaks in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 7.2 MHzand the intensity is −1.3 dB, at the second peak (peak 2), the frequencyis 13.4 MHz and the intensity is 0.1 dB and at the third peak (peak 3),the frequency is 18.6 MHz and the intensity is −1.0. Further, thefrequency component at the frequency (12.3 MHz) same as the centerfrequency in the transmission frequency band of the ultrasound probe Ahas the intensity of −0.5 dB. The spectrum of the transmissionultrasound which is output due to the pulse signal of the drive waveform2 being applied to the ultrasound probe A is shown in FIG. 16.

Comparison Example 1

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 9A, and this is referred to as the drive waveform 3.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 9B. In FIG. 9A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG. 9B,the horizontal axis indicates frequency and the vertical axis indicatessignal intensity. When frequency analysis is performed on this drivewaveform, the minimum frequency at −20 dB is 0.6 MHz, the maximumfrequency at −20 dB is 22.8 MHz and the center frequency is 11.7 MHz.Further, this drive waveform gives one intensity peak in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 9.8 MHzand the intensity is −0.4 dB. Further, the frequency component at thefrequency (12.3 MHz) same as the center frequency in the transmissionfrequency band of the ultrasound probe A has the intensity of −1.0 dB.The spectrum of the transmission ultrasound which is output due to thepulse signal of the drive waveform 3 being applied to the ultrasoundprobe A is shown in FIG. 17.

Comparison Example 2

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 10A, and this is referred to as the drive waveform 4.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 10B. In FIG. 10A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG.10B, the horizontal axis indicates frequency and the vertical axisindicates signal intensity. When frequency analysis is performed on thisdrive waveform, the minimum frequency at −20 dB is 0.2 MHz, the maximumfrequency at −20 dB is 114 MHz and the center frequency is 57 MHz.Further, this drive waveform gives one intensity peak in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 3.4 MHzand the intensity is −2.2 dB. Further, the frequency component at thefrequency (12.3 MHz) same as the center frequency in the transmissionfrequency band of the ultrasound probe A has the intensity of −2.3 dB.The spectrum of the transmission ultrasound which is output due to thepulse signal of the drive waveform 4 being applied to the ultrasoundprobe A is shown in FIG. 18.

Embodiment Example 3

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used. Further, the drive waveform of the pulsesignal output from the transmission unit 12 is the same as the drivewaveform 1 in Embodiment example 1.

Embodiment Example 4

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used. Further, the drive waveform of the pulsesignal output from the transmission unit 12 is the same as the drivewaveform 2 in Embodiment example 2.

Embodiment Example 5

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 11A, and this is referred to as the drive waveform 5.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 11B. In FIG. 11A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG.11B, the horizontal axis indicates frequency and the vertical axisindicates signal intensity. When frequency analysis is performed on thisdrive waveform, the minimum frequency at −20 dB is 2.6 MHz, the maximumfrequency at −20 dB is 22.8 MHz and the center frequency is 12.7 MHz.Further, this drive waveform gives three intensity peaks in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 5.8 MHzand the intensity is 3.8 dB, at the second peak (peak 2), the frequencyis 13.2 MHz and the intensity is 2.0 dB and at the third peak (peak 3),the frequency is 19.2 MHz and the intensity is 1.4. Further, thefrequency component at the frequency (12.3 MHz) same as the centerfrequency in the transmission frequency band of the ultrasound probe Ahas the intensity of 1.1 dB. The spectrum of the transmission ultrasoundwhich is output due to the pulse signal of the drive waveform 5 beingapplied to the ultrasound probe A is shown in FIG. 19.

Embodiment Example 6

As for the above mentioned ultrasound probe 2, an ultrasound probehaving the following characteristics is used, the characteristics being:the minimum frequency (FL20) at −20 dB in transmission is 4.9 MHz; themaximum frequency (FH20) at −20 dB in transmission is 19.7 MHz; thecenter frequency (FC20) is 12.3 MHz and the fractional bandwidth at −20dB in transmission is 120%. This ultrasound probe is referred to as theultrasound probe B. The line Bin FIG. 6 shows the transmission bandwidthshape of the ultrasound probe B.

The drive waveform of the pulse signal output from the transmission unit12 is same as the drive waveform 5 in Embodiment example 5. This drivewaveform gives three intensity peaks in the transmission frequency band(4.9 MHz-19.7 MHz) at −20 dB of the ultrasound probe B. At the firstpeak (peak 1), the frequency is 5.8 MHz and the intensity is 3.8 dB, atthe second peak (peak 2), the frequency is 13.2 MHz and the intensity is2.0 dB and at the third peak (peak 3), the frequency is 19.2 MHz and theintensity is 1.4. Further, the frequency component at the frequency(12.3 MHz) same as the center frequency in the transmission frequencyband of the ultrasound probe B has the intensity of 1.1 dB.

Embodiment Example 7

As for the ultrasound probe 2, an ultrasound probe having the followingcharacteristics is used, the characteristics being: the minimumfrequency (FL20) at −20 dB in transmission is 5.6 MHz; the maximumfrequency (FH20) at −20 dB in transmission is 19.1 MHz; the centerfrequency (FC20) is 12.3 MHz and the fractional bandwidth at −20 dB intransmission is 109%. This ultrasound probe is referred to as theultrasound probe C. The line C in FIG. 6 shows the transmissionbandwidth shape of the ultrasound probe C.

The drive waveform of the pulse signal output from the transmission unit12 is same as the drive waveform 5 in Embodiment example 5. This drivewaveform gives three intensity peaks in the transmission frequency band(5.6 MHz-19.1 MHz) at −20 dB of the ultrasound probe C. At the firstpeak (peak 1), the frequency is 5.8 MHz and the intensity is 3.8 dB, atthe second peak (peak 2), the frequency is 13.2 MHz and the intensity is2.0 dB and at the third peak (peak 3), the frequency is 19.2 MHz and theintensity is 1.4. Further, the frequency component at the frequency(12.3 MHz) same as the center frequency in the transmission frequencyband of the ultrasound probe C has the intensity of 1.1 dB.

Embodiment Example 8

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 12A, and this is referred to as the drive waveform 6.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 12B. In FIG. 12A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG.12B, the horizontal axis indicates frequency and the vertical axisindicates signal intensity. When frequency analysis is performed on thisdrive waveform, the minimum frequency at −20 dB is 2.2 MHz, the maximumfrequency at −20 dB is 22.6 MHz and the center frequency is 12.4 MHz.Further, this drive waveform gives three intensity peaks in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 5.6 MHzand the intensity is 2.2 dB, at the second peak (peak 2), the frequencyis 13.2 MHz and the intensity is 3.7 dB and at the third peak (peak 3),the frequency is 19.2 MHz and the intensity is 3.1. Further, thefrequency component at the frequency (12.3 MHz) same as the centerfrequency in the transmission frequency band of the ultrasound probe Ahas the intensity of 3.1 dB. The spectrum of the transmission ultrasoundwhich is output due to the pulse signal of the drive waveform 6 beingapplied to the ultrasound probe A is shown in FIG. 20.

Embodiment Example 9

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 has a drive waveformas shown in FIG. 13A, and this is referred to as the drive waveform 7.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 13B. In FIG. 13A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG.13B, the horizontal axis indicates frequency and the vertical axisindicates signal intensity. When frequency analysis is performed on thisdrive waveform, the minimum frequency at −20 dB is 3.2 MHz, the maximumfrequency at −20 dB is 23.0 MHz and the center frequency is 13.1 MHz.Further, this drive waveform gives three intensity peaks in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 6.2 MHzand the intensity is 5.0 dB, at the second peak (peak 2), the frequencyis 13.2 MHz and the intensity is 3.7 dB and at the third peak (peak 3),the frequency is 20.2 MHz and the intensity is −0.1. Further, thefrequency component at the frequency (12.3 MHz) same as the centerfrequency in the transmission frequency band of the ultrasound probe Ahas the intensity of 2.9 dB. The spectrum of the transmission ultrasoundwhich is output due to the pulse signal of the drive waveform 7 beingapplied to the ultrasound probe A is shown in FIG. 21.

Comparison Example 3

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used.

A pulse signal output from the transmission unit 12 is a drive waveformas shown in FIG. 14A, and this is referred to as the drive waveform 8.The frequency power spectrum obtained by performing frequency analysison this drive waveform is shown in FIG. 14B. In FIG. 14A, the horizontalaxis indicates time and the vertical axis indicates voltage. In FIG.14B, the horizontal axis indicates frequency and the vertical axisindicates signal intensity. When frequency analysis is performed on thisdrive waveform, the minimum frequency at −20 dB is 0.4 MHz, the maximumfrequency at −20 dB is 9.8 MHz and the center frequency is 5.1 MHz.Further, this drive waveform gives one intensity peak in thetransmission frequency band (3.4 MHz-21.2 MHz) at −20 dB of theultrasound probe A. At the first peak (peak 1), the frequency is 4.2 MHzand the intensity is 7.0 dB. Further, the frequency component at thefrequency (12.3 MHz) same as the center frequency in the transmissionfrequency band of the ultrasound probe A has the intensity of −25.6 dB.The spectrum of the transmission ultrasound which is output due to thepulse signal of the drive waveform 8 being applied to the ultrasoundprobe A is shown in FIG. 22.

Comparison Example 4

As for the ultrasound probe 2, the ultrasound probe A same as that inEmbodiment example 1 is used. Further, the drive waveform of the pulsesignal output from the transmission unit 12 is the same as the drivewaveform 4 in Comparison example 2.

<Evaluation Method>

In an acoustic equivalent member same as RMI 404GS-LE0.5 manufactured byGammex, 50 μm SUS wire is embedded at the 15 mm depth position. Withrespect to each of Embodiment example 1, Embodiment example 2,Comparison example 1 and Comparison example 2, a pulse signal of a drivewaveform having the conditions shown in Table 1 is applied to theultrasound probe and transmission and reception of ultrasound isperformed, and an ultrasound image based on fundamental waves isobtained on the basis of the received signals obtained from the receivedultrasound. On the other hand, with respect to each of Embodimentexample 3 to Embodiment example 9, Comparison example 3 and Comparisonexample 4, the first pulse signal of a drive waveform having theconditions shown in Table 1 and the second pulse signal whose polarityis the inverse of that of the first pulse signal are applied to the samescanning line of the ultrasound probe with time interval therebetweenand transmission and reception of the first ultrasound and the secondultrasound is performed. Then, the received signals obtained from thereceived first ultrasound and the received second ultrasound arecombined by pulse inversion and an ultrasound image of THI (TissueHarmonic Imaging) is obtained. At this time, the transmission focalpoint is at 15 mm. Further, the wire visualization brightness at thetime of imaging is converted into acoustic intensity (dB) and 20 dBresolution (distance resolution, azimuth resolution) is obtained.Further, two frames of ultrasound images are obtained as describedabove, correlation between these two frames of ultrasound images isobtained, depth where this correlation is smaller than 0.5 is specifiedand this is set as the depth. Under their conditions in individualEmbodiment examples 1 to 9 and Comparison examples 1 to 4, a wrist, ametacarpo phalangeal joint flexor tendon, a long head of biceps brachiitendon and a medial meniscu are vidualized. Then, they were evaluatedbased on the following evaluation criterion by the total of ten medicaldoctors and medical technologists who work in the fields related toorthopedics, and the values are averaged to obtain creation scores.

[Evaluation Criterion]

10: at the level excellent for recognizing the tissue condition8: at the level practically sufficient for recognizing the tissuecondition6: not good but at the level where the tissue condition is recognizable4: at the level where recognition of the tissue condition may be aproblem2: at the level where recognition of the tissue condition is difficult

These evaluation criterion are shown in the following table 1.

TABLE 1 ultrasound probe center of drive waveform bandwidth bandwidthfractional center of at −20 dB in at −20 dB in bandwidth bandwidthbanckwidth transmission transmission at −20 dB in at −20 dB at −20 dBdisplay mode No. (MHz) (MHz-MHz) transmission No. (MHz) (MHz-MHz)Embodiment fundamental A 12.3 3.4-21.2 145% 1 9.7 0.6-20  example 1 waveEmbodiment 2 13.8 0.4-27.2 example 2 Comparison 3 11.7 0.6-22.8 example1 Comparison 4 57 0.2-114  example 2 Embodiment THI A 12.3 3.4-21.2 145%1 9.7 0.6-20  example 3 Embodiment 2 13.8 0.4-27.2 example 4 Embodiment5 12.7 2.6-22.8 example 5 Embodiment B 12.3 4.9-19.7 120% example 6Embodiment C 12.3 5.6-19.1 109% example 7 Embodiment A 12.3 3.4-21.2145% 6 12.4 2.2-22.6 example 8 Embodiment 7 13.1 3.2-23.0 example 9Comparison 8 5.1 0.4-9.8  example 3 Comparison 4 57 0.2-114  example 4center of bandwidth drive waveform at −20 dB in probe peak 1 peak 2 peak3 transmission (MHz) MHz dB MHz dB MHz dB MHz dB Embodiment 5.2 −2.014.8 1.2 — — 12.3 −0.4 example 1 Embodiment 7.2 −1.3 13.4 0.1 18.6 −1.012.3 −0.5 example 2 Comparison 9.8 −0.4 — — — — 12.3 −1.0 example 1Comparison 3.4 −2.2 — — — — 12.3 −2.3 example 2 Embodiment 5.2 −2.0 14.81.2 — — 12.3 −0.4 example 3 Embodiment 7.2 −1.3 13.4 0.1 18.6 −1.0 12.3−0.5 example 4 Embodiment 5.8 3.8 13.2 2.0 19.2  1.4 12.3 1.1 example 5Embodiment example 6 Embodiment example 7 Embodiment 5.6 2.2 13.2 3.719.2  3.1 12.3 3.1 example 8 Embodiment 6.2 5.0 13.2 3.7 20.2 −0.1 12.32.9 example 9 Comparison 4.2 7.0 — — — — 12.3 −25.6 example 3 Comparison3.4 −2.2 — — — — 12.3 −2.3 example 4 image quality evaluation resultdistance azimuth metacarpo long head of resplution resolutionpenetration phalangeal joint biceps brachii medial display mode (μm)(μm) (mm) wrist flexor tendon tendon meniscu Embodiment fundamental 308677 59 8.2 8.4 7.3 7.0 example 1 wave Embodiment 312 660 65 8.6 8.8 7.87.3 example 2 Comparison 456 630 42 6.4 7.0 5.9 4.8 example 1 Comparison315 655 57 8.2 8.5 7.7 7.1 example 2 Embodiment THI 285 645 54 8.9 8.97.8 7.6 example 3 Embodiment 240 632 55 9.4 9.6 8.4 8.0 example 4Embodiment 225 651 59 9.6 9.7 8.8 8.2 example 5 Embodiment 278 643 539.0 9.0 8.0 7.6 example 6 Embodiment 341 638 47 7.7 7.4 7.5 7.0 example7 Embodiment 299 662 53 8.6 8.8 8.4 7.7 example 8 Embodiment 330 668 548.2 8.3 8.0 7.5 example 9 Comparison 512 598 40 5.6 5.9 5.2 5.0 example3 Comparison 320 680 48 8.1 8.0 7.3 6.6 example 4

<Evaluation Results>

From the results shown in Table 1, it is understood that Embodimentexamples 1 to 9 exhibit good distance resolution and greater penetrationcomparing to Comparison examples 1 and 3 where ultrasound transmissionand reception is performed with pulse signals of the drive waveforms 3and 8, respectively. Further, with respect to Embodiment examples 1 to9, their visualization evaluations of a wrist, a metacarpo phalangealjoint flexor tendon, a long head of biceps brachii tendon and a medialmeniscu are higher comparing to Comparison examples 1 and 3.

In a case where ultrasound transmission and reception is performed witha pulse signal of the drive waveform 4, although Comparison examples 2and 4 do not exhibit specific inferiority in their ultrasound imagesbased on fundamental waves, in terms of ultrasound images obtained basedon THI, their visualization evaluations, especially in a medial meniscu,are low comparing to Embodiment examples 3 to 9.

As described above, in the embodiment, the ultrasound probe 2 outputstransmission ultrasound toward a subject by a pulse signal being inputand outputs received signals by receiving reflected ultrasound from thesubject. The transmission unit 12 outputs a pulse signal of a drivewaveform formed of rectangular waves to make the ultrasound probe 2generate transmission ultrasound. With respect to the frequency powerspectrum of the pulse signal, there are intensity peaks in a frequencyband included in the transmission frequency band at −20 dB of theultrasound probe 2 on the low frequency side and the high frequency sideof the center frequency in the transmission frequency band, and also,intensities in the frequency regions between the plurality of intensitypeaks are −20 dB or greater with the maximum intensity value among theintensity peaks being the reference. As a result, there is no need toadd a complicated circuit for forming a waveform of a pulse signal, andhigh resolution can be maintained in transmission ultrasound at lowcost. Further, with respect to an ultrasound image based on fundamentalwaves, since an ultrasound waveform of high amplitude and short pulsescan be obtained, penetration can be improved by the low frequencycomponent being increased while maintaining high resolution.

Moreover, according to the embodiment, the transmission unit 12 outputspulse signals having different drive waveforms for a plurality of timeson the same scanning line with time intervals therebetween. The imagegeneration unit 14 combines the received signals each of which obtainedfrom reflected ultrasound of the transmission ultrasound generated byeach output of pulse signal, and generates ultrasound image data on thebasis of the composite pulse signal. As a result, since a harmonic canbe received in a broadband by pulse inversion, an ultrasound image inwhich resolution is even more improved can be obtained at a low cost.

Further, according to the embodiment, in the frequency power spectrum ofthe pulse signal, the intensity of the frequency component at at leastany one of the plurality of intensity peaks is greater than theintensity of the frequency component at the frequency same as the centerfrequency in the transmission frequency band at −20 dB of the ultrasoundprobe 2. As a result, ultrasound can be transmitted in a bandwidthbroader than the transmission bandwidth of the ultrasound probe and theresolution can be improved.

Furthermore, according to the embodiment, in the frequency powerspectrum of a pulse signal, there are two or more intensity peaks on thehigh frequency side of the center frequency in the transmissionfrequency band at −20 dB of the ultrasound probe 2, the intensity peaksbeing included in the transmission frequency band. As a result,ultrasound having broader bandwidth on the high frequency side can betransmitted and the resolution can be improved.

Moreover, according to the embodiment, since a pulse signal is formed ofrectangular waves of five values or less, resolution can be improved ata low cost.

Further, according to the embodiment, since the fractional bandwidth at−20 dB is 110% or greater in the ultrasound probe 2, ultrasound of evenhigher resolution can be transmitted.

The Description of the embodiment of the present invention is merely anexample of an ultrasound diagnostic imaging apparatus according to thepresent invention and the present invention is not limited to what isdescribed. The detail configuration and detail operations of thefunctional parts which constitute the ultrasound diagnostic imagingapparatus can be modified arbitrarily.

The entire disclosure of Japanese Patent Application No. 2013-041380filed on Mar. 4, 2013 is incorporated herein by reference in itsentirety.

What is claimed is:
 1. An ultrasound diagnostic apparatus, comprising:an ultrasound probe which outputs transmission ultrasound correspondingto a drive signal, which receives reflected ultrasound from the subjectand which outputs a received signal according to the reflectedultrasound; a drive signal outputter which outputs the drive signal tothe ultrasound probe; a hardware processor which controls the drivesignal outputter to output a first drive signal having a first drivewaveform and a second drive signal having a second drive waveform thatis different from the first drive waveform; a received signal generatorwhich generates a first received signal based on the reflectedultrasound corresponding to the transmission ultrasound that is outputbased on the first drive signal and a second received signal based onthe reflected ultrasound corresponding to the transmission ultrasoundthat is output based on the second drive signal; and an extractor whichextracts by arithmetic of the first received signal and the secondreceived signal a received signal component which to be used in imaging,wherein frequency spectrums of the first drive signal and the seconddrive signal have a first intensity peak on a low frequency side of acenter frequency of the transmission frequency, a second intensity peakon a high frequency side of the center frequency and a third intensitypeak at a frequency between a frequency corresponding to the firstintensity peak and a frequency corresponding to the second intensitypeak, in a frequency band included in a transmission frequency band at−20 dB of the ultrasound probe.
 2. The ultrasound diagnostic apparatusof claim 1, wherein the extractor extracts the imaging received signalcomponent by adding the first received signal and the second receivedsignal.
 3. The ultrasound diagnostic apparatus of claim 1, wherein thetransmission ultrasound which is output based on the first drive signaland the transmission ultrasound which is output based on the seconddrive signal are output on a same scanning line with a time intervaltherebetween.
 4. The ultrasound diagnostic apparatus of claim 1, whereinat least one of the first intensity peak, the second intensity peak andthe third intensity peak is greater than an intensity of a frequencycomponent at a frequency same as the center frequency in thetransmission frequency band at −20 dB of the ultrasound probe.
 5. Theultrasound diagnostic apparatus of claim 1, wherein a fractionalbandwidth at −20 dB is 110% or greater in the ultrasound probe.
 6. Theultrasound diagnostic apparatus of claim 1, wherein the second drivesignal has polarity which is the inverse of polarity of the first drivesignal.
 7. The ultrasound diagnostic apparatus of claim 1, wherein eachof the first drive signal and the second drive signal is a pulse signal.8. The ultrasound diagnostic apparatus of claim 1, wherein the imagingreceived signal component is a harmonic component.